1. Field of the Invention
The present invention relates generally to electro-magnetic transducers and, more particularly, to electro-magnetic transducers that are self-cooled by means of instantaneous pressure changes created by the natural motion of the transducer coil and the bobbin on which it is wound.
2. Description of the Prior Art
There are many electro-magnetic transducers on the market that were designed for the purpose of self-cooling. However, some of those designs are very expensive and their cost makes them unmarketable, there are others that produce marginal cooling, and still others that offer virtually no cooling. Most common designs include a vertical venting passage through the center of the pole piece of the electro-magnetic motor of loudspeakers. The vertical passage, during an outward stroke of the voice coil of the electro-magnetic motor causes cold air to be sucked from beneath the electro-magnetic motor into the vertical passage and up underneath the loudspeaker dust cap; and during the inward stroke of the voice coil the hot air beneath the dust cap is expelled from the region of the electro-magnetic motor and then the system is ready for another cycle on the next outward stoke of the voice coil. Unfortunately, these types of a cooling systems only provide cooling of the inside surface of the vertical passage of the pole piece with the temperature of the voice coil only reduced by the inefficient convection of heat transferred from the voice coil to the pole piece and by conduction from the outside of the pole piece to the inside of the voice coil. Thermal cooling in this way is limited by to free air convection, i.e., heat convection through the air between the voice coil and the pole piece.
The speaker design in U.S. Pat. No. 5,357,586 by Nordschow teaches mounting the speaker motor below the bottom of the basket to a ring that has spaced apart venturi passages that open into the cavity above the top plate of the motor and below the spider. Additionally, venturi passages are formed through the lower center of the pole piece in communication with the gap through which the voice coil travels with the venturi passages on one side of the pole piece opening into the voice coil gap and on the other side of the pole piece opening to the center of the pole piece. Additionally, an aerodynamically shaped body is inserted into the top of the pole piece with the smaller end extending into the center of the pole piece while defining a narrow ring passage around the top edge of the pole piece and the larger end on the aerodynamically shaped body thus creating a venturi passage opening into the lower center of the pole piece from the cavity below the dust cap. This design is thus limited to the use of a special speaker basket, only mounting the speaker motor to the outside bottom of the basket, and the machining of the opposing venturi passages through the interior bottom portion of the pole piece. Thus this design requires expensive machining of the pole piece and greatly limits variations on the design of the completed speakers that can utilize this cooling technique making it very impractical for all of those reasons.
The speaker design in U.S. Pat. No. 5,909,015 by Yamamoto el al. teaches the importance of loud speaker cooling, specifically self-cooling. Yamamoto's approach to self cooling is to push and pull air through narrow pathways that are carved out of the top plate and the bottom plates of the electro-magnetic motor with those pathways being perpendicular to the axis of movement of the voice coil. These plates are typically steel and therefore expensive to machine. This attempted solution creates turbulent air flow and wind noise 90° off the axis of movement of the voice coil. Additionally, the holes in the top/bottom plates provide a major pathway for metal debris to cross into the magnetic gap. This is an eminent situation that will destroy the speaker once the debris reaches the voice coil. During speaker installation is very likely that the installer will place the speaker in an environment that contains metal debris as it is often necessary to grind metal pieces to enlarge a hole in the location in which the speaker is to be installed (e.g., in car installations). The metal debris will be attracted to the outside ring of the bottom and the top magnet plates. During airflow these debris will migrate into the magnetic gap through these large openings.
In U.S. Pat. Nos. 6,330,340 and 6,327,371, both by Proni, the speaker design includes a vented collar placed between the voice coil and the cone (diaphragm). Those vents through the collar allow air to be sucked into a cavity below the dust cap and blown out through the vents as the volume of that cavity changes during operation of the speaker, the vents in the collar allow the air to travel in and out of the cavity below the dust cap to improve the cooling system. This design is too complex and does not deal with forced air cooling. Air is allowed into the cavity below the dust cap without being forced directly to the hottest component of the electro-motive motor, i.e. the voice coil.
In U.S. Pat. No. 6,243,479, also by Proni, which is similar to the cooling technique of U.S. Pat. No. 5,357,586 discussed above, shows a pole piece cooling system that includes a cavity located in the pole piece through which the voice coil passes. This design has a major problem that makes the speaker unattractive due to the highly audible noise that the highly turbulent air flow that it creates. Additionally, this solution is expensive to manufacture.
In U.S. Pat. No. 5,497,428 by Rojas the cooling system includes a vented pole piece that directs air flow between the center of the pole piece and the gap through which the voice coil travels. To implement this design, the pole piece is a complex structure formed with the top of the center passage closed by a conical structure to direct the air flow to and from a plurality of passages machined through the side of the pole piece in communication with the gap through which the voice coil passes. Further those holes through the side of the pole piece causes a major reduction in the flux density in the gap. This cooling solution is too expensive and complex in its execution, moreover, the Rojas solution, as well as the Proni solutions, each delivers cooling air to the voice coil from openings that are below the top plate of the electro-magnet of the electro-magnetic motor of the loudspeaker. Under the top plate, the side pathways are very narrow and thermal conductivity is at its maximum only when the voice coil is in its most outward position.
Thus a speaker cooling design is needed that does not require expensive machined parts or a special basket. One that can be used with a variety of speaker designs with few limitations. The present invention provides such a design.